Intramedullary alignment guide

ABSTRACT

An intramedullary alignment guide and method for use thereof are disclosed for accurately preparing and shaping the distal femur end surface to receive a knee prosthesis for securement thereto. The guide references the femur intramedullary canal to ensure that a distal femoral resector is properly positioned at a selected angle with respect to a patient&#39;s mechanical axis. In the preferred embodiment, the intramedullary alignment guide includes an opening for inserting an intramedullary rod therethrough and into the intramedullary canal of a patient. The present guide includes an adjustment mechanism which allows a surgeon to quickly and easily deflect an attached distal femoral resector into a desired angular displacement with respect to intramedullary canal. In accordance with the preferred method, the distal femoral resector angled with respect to the intramedullary canal so that a cut can be made in a patient&#39;s distal femur end which is perpendicular with the patient&#39;s mechanical axis. The present guide can be used on patients having various anatomies, and in operations involving both the right and left legs. A sighting tool is also disclosed which allows a surgeon to externally verify that the distal femoral resector is properly aligned with the patient&#39;s mechanical axis.

This is a continuation of application Ser. No. 08/357,430 filed Dec. 16,1994, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to medical instruments and a method for usepertaining particularly to an improved intramedullary alignment guidefor accurately preparing and shaping the distal femur end surface toreceive a knee prosthesis to be secured thereto.

2. Description of Related Art

Knee surgery for the replacement and repair of knee joints has becomecommonplace in recent years. Total knee replacement systems andprostheses are available from a variety of manufacturers. Such totalknee replacement systems, when properly installed, approximate thepatient's natural knee movement. However, all knee prosthetic devicesneed to be properly fitted and installed to achieve an optimum fit andalignment. Proper alignment of the prosthetic device is critical to thesuccessful outcome of a total knee replacement surgery. It is well knownthat it is desirable to provide an effective system of instruments andmethods which ensure that the distal femur end is properly prepared forreceiving the prosthetic device.

Some prior art systems have been developed which purport to assist asurgeon in preparing distal femur and proximal tibia ends for receivingknee prosthetic devices. One such system is shown in Petersen, U.S. Pat.No. 4,524,766. Petersen teaches a surgical knee alignment and cuttingguide system which references a patient's mechanical axis, and from thatreference, provides a cutting guide for shaping the patient's proximaltibia to receive the tibia portion of a knee prosthesis. Cutting guidesare referenced from the tibia components of the knee prostheses forshaping the distal femur end to receive the femur portion of the kneeprostheses. However, referencing from the patient's tibia introducesinaccuracies into the prosthetic alignment process. It is thereforedesirable to provide an alignment system which references directly fromthe patient's distal femur end and provides for locating the patient'smechanical axis from the anatomic axis. By referencing from thepatient's mechanical axis, an improved alignment system should employ analignment guide and cutting guide to properly prepare the distal femurend for receiving the knee prosthetic device.

Another system for shaping the distal femur end is taught in Dunn, etal., U.S. Pat. No. 4,759,350. Dunn teaches a system of instruments forshaping the distal femur and proximal tibia surfaces to receivecomponents of a knee prosthesis for knee replacement surgery. The Dunnsystem determines a patient's mechanical axis with reference to thepatient's anatomic axis by using an alignment guide that is adapted tofit into a hole drilled into the distal femur end and intersecting thefemoral intramedullary canal. Cutting guides or distal femoral resectorsare attached to the alignment guide and are used to prepare the distalfemur end to receive the femur portion of the prosthetic device.

The Dunn alignment guide is used to align the distal femoral resector orcutting guide so that a cut can be made in the distal femur end so as toprovide a flattened bone end surface which is perpendicular to thepatient's mechanical axis. The cut in the distal femur end is based upona determination of the relative angular displacement of the patient'smechanical axis from the patient's anatomic axis. To enable a surgeon tocut the distal femur end properly and at the appropriate angle withrespect to the mechanical axis, the distal femoral cutting guide isdisplaced relative to the intramedullary alignment guide such that acutting slot in the cutting guide is exactly perpendicular to thepatient's mechanical axis. The distal femoral cutting guide is securedto the alignment guide using a plurality of pins. A surgeon can pivotthe cutting guide such that a cutting slot in the cutting guide isexactly perpendicular to the patient's mechanical axis. A pivot pin isfitted into the distal femoral cutting guide to allow the guide to pivotslightly with respect to the intramedullary alignment guide. The surgeonuses an alignment pin which may be inserted through one of a pluralityof holes in the distal femoral cutting guide to achieve the desiredangular displacement between the cutting guide and the alignment guide.

Disadvantageously, the system taught by Dunn requires that the distalfemoral cutting guide pivot about the medial condyle of the femur when asurgeon inserts an alignment pin through one of the plurality of holesin the cutting guide and into the alignment guide. By pivoting about themedial condyle of the femur, and not about the intramedullary canal, theDunn system increases the length of the cut across the distal femur endas the angular displacement between the distal femoral cutting guide andthe alignment guide is increased. Conversely, as the angulardisplacement between the cutting guide and the alignment guide isdecreased, due to a small angular displacement between the patient'sanatomic and mechanical axes, the length of the cut in the distal femurend is correspondingly decreased. Therefore, there is a need for animproved intramedullary alignment guide which provides proper angulationof the prepared distal femur end yet allows the distal femoral resectoror cutting guide to be pivoted about the patient's intramedullary canal.

To ensure that proper limb alignment is restored to a patient, acombination of intramedullary alignment devices and extramedullaryalignment check rods have been used. The combination of intramedullaryalignment devices and extramedullary alignment check rods increase theprobability for a successful clinical outcome.

The prior art systems for preparing distal femur ends for receiving kneeprosthetic devices are difficult to assemble, require an inventoryhaving a number of small, easily lost components, and requiresignificant operating-room time for their use. For example, the systemtaught by Dunn includes a femoral alignment guide, an anterior femoralcutting guide with locator, a distal femoral cutting guide, an APmeasuring guide, a femoral finishing guide, and a system for preparingthe proximal tibia end. A surgeon, after opening the damaged knee area,sequentially uses these instruments to prepare a patient's distal femurand proximal tibia ends to receive knee components of a selectedprosthetic device. The various components taught by Dunn are difficultto assemble, and have a number of components which may be lost ormisplaced during use and storage. For example, the Dunn system requiresuse of a pivot pin, an alignment pin, and a plurality of additional pinswhich are used to secure the distal femoral cutting guide in place afteralignment. These pins have proven difficult to use as they are small andnumerous, and hence easily misplaced.

Therefore, there is a need for an improved intramedullary alignmentguide which facilitates quick and accurate alignment guide rotation, hasno loose parts, no loose pins, is easily assembled, and which thereforereduces the amount of operating-room time necessary to use. The presentinvention provides such an improved intramedullary alignment guide.

SUMMARY OF THE INVENTION

The present invention is an intramedullary (IM) alignment guide andmethod for use thereof which provides a means for aligning a distalfemoral resector or cutting guide with the mechanical axis of a patient.Using the patient's intramedullary canal as a reference, the present IMguide provides a mechanism for ensuring that a surgeon positions adistal femoral resector perpendicular with the patient's mechanicalaxis. Using the present invention, a surgeon can quickly and easilyalign a distal femoral resector with the patient's mechanical axis bypositioning the resector into a selected angle relative to the patient'sanatomic axis. The present invention includes an adjustment mechanismwhich includes an adjustment rod, a rocker unit, and displacement pins.The adjustment rod includes a plurality of notches having inscriptionswhich correspond to the desired angular displacement of the distalfemoral resector and the adjustment rod. By inserting an IM rod throughthe adjustment rod and into the patient's IM canal, and subsequentlyrotating the adjustment rod into a selected notch, the surgeon causesthe displacement pins to deflect the distal femoral resector into adesired angular displacement with the adjustment rod. Thus, the surgeoncan quickly and easily align the distal femoral resector so that a cutcan be made in the patient's distal femur end which is perpendicularwith the patient's mechanical axis.

The present IM guide accommodates various patient anatomies. The IMguide is relatively light and compact, easily assembled, and can be usedto align cutting guides for both right and left knee surgeries. Thepresent invention also includes an external alignment checking systemhaving a quick attach/quick release sighting tool. The sighting toolincludes a plurality of openings which allows the surgeon to verifywhether the distal femoral resector is properly aligned with thepatient's mechanical axis. If the resector is not properly aligned, thesurgeon can easily realign the resector using the adjustment rod of thepresent invention. The realignment process is greatly simplified usingthe present invention because the surgeon does not need to disassembleand reassemble the alignment guide, nor does the surgeon need to removethe distal femoral cutting guide. Hence, the present invention reducesthe overall operating room time and the costs related to knee surgery.

The details of the preferred embodiment of the present invention are setforth in the accompanying drawings and the description below. Once thedetails of the invention are known, numerous additional innovations andchanges will become obvious to one skilled in the art.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A, 1B and 1C show the angular displacements between themechanical and anatomic axes of three different human legs as determinedfrom a developed radiograph of the three legs.

FIG. 2 shows a rear perspective view of the preferred embodiment of thepresent intramedullary (IM) alignment guide.

FIG. 3 shows an exploded view of the IM alignment guide of FIG. 2.

FIG. 4 shows a partial cut-away and cross-sectional view of the presentinvention showing details of the rocker unit, the displacement pins, andthe base.

FIG. 5 shows the IM alignment guide of FIGS. 2-4 having an IM rodinserted through the IM guide and into the IM canal of a patient.

FIG. 6 shows a front perspective view of the IM guide of FIG. 5 having aquick attach/quick release sighting tool for externally verifying properalignment of the guide with the patient's mechanical axis.

FIGS. 7a and 7b show details of the attach and release mechanism used toattach and release the sighting tool shown in FIG. 6 to a distal femoralresector.

Like reference numbers and designations in the various drawings refer tolike elements.

DETAILED DESCRIPTION OF THE INVENTION

Throughout this description, the preferred embodiment and examples shownshould be considered as exemplars, rather than as limitations on thepresent invention.

Patient Preparation and Anatomical Considerations

The present invention is preferably used to perform knee surgery on apatient, such as total knee replacement or arthroplasty. The success ofa total knee replacement procedure is directly dependent uponre-establishing normal lower extremity alignment to the patient. Toensure that proper limb alignment is restored to the patient, thepresent invention provides an intramedullary guide that allows a surgeonto quickly and accurately align a distal femoral resector such that acut can be made in the distal femur end which is perpendicular to thepatient's mechanical axis.

As is well known, a patient's mechanical axis is preferably establishedby drawing a line on an appropriate x-ray of a patient from thepatient's hip, through the patient's knee, and to the patient's anklewhen the patient is in a stable and erect position. FIG. 1 shows thefemur and tibia bones of 3 different human legs 100, 112, and 120,wherein each leg has a different angular displacement between itsrespective mechanical and anatomic axes. As shown in FIG. 1, themechanical and anatomic axes of each patient can be determined from adeveloped radiograph of a patient's leg. More specifically, themechanical axis of the leg 100 is determined by drawing a line from thecenter of the femoral head 102 to the center of the distal femur at theknee 104. The mechanical axis of leg 100 is referred to in FIG. 1 by theline 106. The anatomic axis 108 of leg 100 is determined by drawing aline down the middle of the distal femoral shaft. As described in moredetail below, an intramedullary alignment rod is typically fitted withinthe femoral shaft to coincide with and represent the anatomic axis. Theangle between the two axes 106 and 108 is the angle that must bereproduced by the present invention during surgery so that a cut alongthe distal femur end 110 is perpendicular to the mechanical axis 106.

The angular difference between the mechanical and anatomic axes has beenfound in practice to typically be between about 5° and 6°. However, dueto differences in patient anatomy, the angular displacement can rangefrom about 3° to 9°. For example, the angular displacement between theanatomic and mechanical axes of the leg 100 is 5°. However, due to abroadened pelvis or significant coxa vara with long femoral necks, thelegs 112 and 120 have angular displacements of 7° and 9°, respectively.The present invention advantageously provides a means for angulating adistal femoral resector by a range of angles relative to the anatomicaxis which accommodates varied patient anatomies.

Once the angular difference between the patient's mechanical andanatomic axes are determined, a properly angled cut can be made in thedistal femur end by referencing the patient's anatomic axis. The femoralcanal, also known as the intramedullary canal, is used to reference thepatient's anatomic axis. By using the intramedullary canal as areference, and having a priori knowledge of the angular displacementbetween the anatomic and mechanical axes, the present invention providesan apparatus and method for aligning a distal femoral resector properlysuch that the distal femur end can be cut at an angle which isperpendicular to the mechanical axis of the patient. Therefore, once theanatomic axis is established, the amount of distal femur bone to beremoved can be calculated, so that the resultant surface bone end formsa plane that is perpendicular to the mechanical axis.

Detailed Description of the Intramedullary Alignment Guide

FIG. 2 shows a rear perspective view of the preferred embodiment 200 ofthe present intramedullary (IM) alignment guide. FIG. 3 shows anexploded view of the IM alignment guide of FIG. 2. Referringsimultaneously to both FIGS. 2 and 3, the IM alignment guide 200preferably comprises a base 202, a distal femoral resector attachmentrod 204, a plurality of pivot pins 206, a cylindrical rocker unit 208, aplurality of displacement pins 210, an adjustment rod 212 having a base214 and a top-facing interlock unit 216, an interlock ring 218, alocking knob 220, and a locking "C" ring 222. The IM alignment guide 200preferably comprises surgical grade, bio-compatible materials, such asstainless steel, titanium, ceramic, structural plastics, etc.Preferably, the IM guide 200 is easily sterilized by known methods, suchas heat sterilization, pressurized gas, and radiation sterilizationmethods. In the preferred embodiment, the base 202 is cut from a solidblock of surgical grade stainless steel and is manufactured so that thetop and bottom faces of the base 202 are substantially parallel to eachother. The bottom face 224 of the base 202 preferably contains aplurality of holes 226 which are formed or drilled through to the topface of the base 202. The purpose of the holes 226 is described in moredetail below with reference to the description of the use of the presentinvention during surgery.

The components which comprise the present invention are shaped to fittogether as shown in FIGS. 2 and 3. As shown in FIG. 2, when assembled,the present IM alignment guide is a compact, easily manipulated unit.When assembled, the components are held in place by the C-ring 222 whichis clamped around a threaded end 230 of the rocker unit 208. Whenassembled, the pins 210 are inserted through a plurality of holes 232which are cut into a base section 234 of the rocker unit 208. Theoperation of the pins 210 and the base 234 is described in more detailbelow with reference to FIG. 4. As shown in FIG. 3, the adjustment rod212 has a substantially hollow interior canal 235 which is shaped toreceive the rocker unit 208. When assembled as shown in FIG. 2, the base214 of the adjustment rod 212 abuts a top surface of the base section234 of the rocker unit 208.

The interlock ring 218 has an inner diameter which is slightly greaterthan the outer diameter of the rocker unit 208 and the threaded end 230.During assembly of the IM guide 200, the interlock ring 218 is slippedover the threaded end 230 of the rocker unit 208 until it rests adjacentthe top unit 216 of the adjustment rod 212. As shown in FIG. 3, theinterlock ring 218 has a knob 245 which extends toward the top unit 216.The top unit 216 includes a plurality of notches 236 which are formedinto a distal surface of the top unit 216. The notches 236 are spacedapart at precise locations on the distal surface of the top unit 216 sothat when the knob 245 is placed into a selected one of the notches 236,the adjustment rod 212 rotates by a fixed degree of rotation. A detaileddescription of the operation of the guide 200, and more particularly theoperation of the adjustment rod 212, the top unit 216, the interlockring 218, and the notches 236, is given below with reference to FIGS.4-6.

The locking knob 220 has a threaded interior channel which mates withthe threaded end 230 of the rocker unit 208. Once the adjustment rod 212and the interlock ring 218 are fitted over the rocker unit 208, thelocking rod 220 is threaded onto the threaded end 230. The threaded end230 includes a narrow slot 240 which extends from a distal end of thethreaded end 230 and is formed lengthwise along the rocker unit 208. Asshown in FIG. 3, the interlock ring 218 includes an inwardly-facinginterlock knob 242 which is shaped to fit within the slot 240 of therocker unit 208. Therefore, when the interlock ring 218 is slipped overthe threaded end 230 of the rocker unit 208, the interlock knob 242mates with the slot 240 and prevents the interlock ring 218 fromrotating about the rocker unit 208. Once the locking knob 220 isthreaded over the threaded end 230 of the rocker unit 208, the C-ring222 is secured to a distal end of the threaded end 230. The C-ring 222prevents the inadvertent disassembly of the IM alignment guide 200during use. The C-ring 222 is preferably positioned on the threaded end230 of the rocker unit 208 such that the locking knob 220 can bedisengaged from the interlock ring 218 thereby allowing the adjustmentrod 212 to be rotated into a desired position.

Referring again to FIG. 3, the base section 234 of the rocker unit 208includes an extension 244 which has an outer diameter that is less thanthe outer diameter of the base section 234. The extension 244 of thebase section 234 preferably includes two threaded holes 246 which arepositioned at opposite sides of the extension 244. The threaded holes246 are shaped to receive the pivot pins 206. The extension 244 of thebase section 234 is inserted within a hole 250 formed through the base202 of the alignment guide 200. During assembly, the extension 244 isinserted within the hole 250 and the pivot pins 206 are threaded throughpivot holes 252 formed in the side walls of the hole 250 and into theholes 246 of the extension 244. When the rocker unit 208 is seated inthe hole 250 by its extension 244, and the pivot pins 206 are threadedinto the holes 246 of the extension 244, the rocker unit 208 pivotsabout the pivot pins 206.

The underside of the base 214 of the adjustment rod 212 includes aninclined annular groove 256. When the guide 200 is assembled as shown inFIG. 2, the adjustment rod 212 rotates about the rocker unit 208 and theinclined annular groove 256 rides upon distal ends of the displacementpins 210. Depending upon the degree of rotational displacement of theadjustment rod 212, the distal ends of the displacement pins 210 contactthe inclined annular groove 256 at different locations along the groove.As described in more detail below with reference to FIG. 4, the pointsof contact between the distal ends of the displacement pins 210 and theinclined annular groove 256 determine the angular displacement of thebase 202 with respect to the rocker unit 208. This angular displacementis used to properly align a distal femoral resector so that thepatient's distal femur end can be cut at an angle which is perpendicularto the patient's mechanical axis.

FIG. 4 shows a cross-sectional view of the present invention showingdetails of the rocker unit 208, the displacement pins 210, and the base202. When the alignment guide 200 is assembled as shown in FIGS. 2 and4, the displacement pins 210 are inserted through the holes 232 formedthrough the base section 234 of the rocker unit 208. One end of eachdisplacement pin 210 abuts against a top surface of the base 202 of thealignment guide 200 as shown in FIG. 4. The other end of eachdisplacement pin 210 fits within the inclined annular groove 256 formedin the underside of the base 214 of the adjustment rod 212. As shown inphantom in FIG. 4 via the dotted line 260, the inclined annular groove256 varies in depth from one side of the base section 214 to theopposite side of the base section 214. More specifically, as shown inFIG. 4, the groove 256 is most shallow at the leftmost position of thebase section 214. The groove 256 is deepest at the rightmost position ofthe base section 214. The angle that the base 202 makes with respect tothe rocker unit 208 varies according to the rotational position of theadjustment rod 212 as it rotates about the rocker unit 208. Because theinclined annular groove 256 varies in depth along the diameter of thebase 214, the displacement of the base 202 caused by the pins 210 variesaccording to the rotational position of the rod 212. The base 202 pivotswith respect to the rocker unit 208 and rod 212 using the pivot pins 206(FIG. 3). The base 202 is deflected at an angle with the rod 212 due tothe degree of displacement produced by the displacement pins 210.

With the adjustment rod 212 first rotated into a starting neutralposition, the displacement pins 210 contact the inclined annular groove256 at contact points which are at equal depth within the base section214. Therefore, at the starting neutral position, the rocker unit 208and rod 212 are perpendicular to the base 202. As the adjustment rod 212is rotated about the rocker unit 208, the displacement pins 210, due tothe varying depth of the inclined annular groove 256, cause the base 202to be deflected into various angles with respect to the rocker unit 208.For example, as shown in FIG. 4, the base 202 is deflected to a maximumangular displacement from the starting neutral perpendicular position.As the adjustment rod 212 is rotated, the positions at which thedisplacement pins 210 contact the inclined annular groove 256 change,and the amount of angular displacement of the base 202 with respect tothe rocker unit 208 and rod 212 created by the displacement pins 210changes accordingly. When the adjustment rod 212 is rotated into aposition which causes the displacement pins 210 to produce an equalmount of linear displacement (i.e., when the points of contact of thedisplacement pins 210 with the inclined annular groove 256 are at equaldepth), the base 202 is returned to a starting neutral angular positionwith respect to the rocker unit 208 (i.e., the base 202 is perpendicularto the rocker unit 208). As the adjustment rod 212 is rotated beyond thestarting neutral position, the displacement pins 210 cause the base 202to form an angle with the rocker unit 208 which is greater than 90°.

During use, the base 202 is placed into a desired angle with respect tothe rocker unit 208 by manually adjusting the knob 212 and securing theknob 212 in the desired position by inserting the knob 245 of theinterlock ring 218 into one of the notches 236 on the adjustment rod212. The device is calibrated so that particular rotational positions ofthe adjustment knob 212 correspond to specific angular displacements. Byselecting one of the rotational positions of the adjustment knob 212 andby inserting the knob 245 into one of the notches 236, the surgeon canquickly and easily change the angle that the base 202 makes with respectto the rocker unit 208. This angle corresponds to the measured angulardisplacement between the anatomic axis and mechanical axis, as describedbelow in more detail with respect to FIGS. 5-7. As described below inmore detail, the present invention accommodates angular displacementsfor both right and left legs.

Knee Surgery Using the IM Guide

As described above with reference to FIG. 1, once the angular differencebetween the patient's mechanical and anatomic axis is determined, thepatient's femur channel or canal, also known as the intramedullary (IM)canal, is used to represent the patient's anatomic axis. A very accuratemethod of femoral component alignment is therefore provided by using thepatient's IM canal as a reference. A pre-operative x-ray film is firsttaken to clearly show the canal on the x-ray. The x-ray is preferably astanding radiograph showing the center of the femoral head, the knee,and as much of the tibia as possible, preferably including the ankle.Alternatively, a single A/P radiograph of the entire femur will allowfor correct calculation of the mechanical and anatomic axis. Once theanatomic and mechanical axes are established, the amount of distal femurremoval may be calculated in a known fashion. The present IM alignmentguide is used to ensure the surgeon that the distal femur end is cut atan angle which is perpendicular to the mechanical axis.

In practice, the patient's knee is prepared in a known manner to receivethe components of a knee prosthesis. The femur and tibia ends areprepared independently, and either one can be prepared first. Inpractice, the distal femur end is routinely prepared first because theresection of the posterior femoral condyles offer greater exposure ofthe proximal tibia, thereby facilitating its preparation.

With the patient's knee opened appropriately and flexed, the site forinserting the intramedullary alignment guide of the present invention isselected on the distal femur, as shown in FIG. 5. The intramedullarycanal of the femur is entered by drilling a hole 302 into the distalfemur end. Care is exercised so that the drill avoids the patient'scortices. The hole drilled in the distal femur end is used for alignmentin accordance with the present invention. Once the intramedullary canalis accessed, an intramedullary (IM) rod 304 is inserted therein. Inpractice, only the cancellous bone of the distal femur needs to bedrilled, as the femur's hollow diaphysis usually provides no resistanceto the insertion of the IM rod 304. The drilled hole 302 is necessaryfor alignment only and is not for component positioning on the distalfemur. The alignment guide 200 is positioned on the distal femur withthe bottom facing surface 224 of the base 202 of the alignment guide 200facing the distal femur, as shown in FIG. 5. As described below in moredetail, the alignment guide 200 is used in conjunction with the IM rod304 to properly position a distal femoral resector or cutting guide 306so that the surgeon can cut the distal femur end perpendicular to themechanical axis. The IM guide 200 may optionally facilitate cutting thedistal femur end at any desired angle with respect to the mechanicalaxis.

The T-shaped IM rod 304 includes a handle 308 and a plurality of flutes310 cut along the length of the rod. The handle 308 of the IM rod allowsa surgeon to easily manipulate the rod 304 during surgery. The flutes310 serve two purposes: (1) they reduce air pressure which ispotentially built up when the rod 304 is inserted within the IM canal,and (2) they serve as a channel for receiving the inwardly-facinginterlock knob 242 described above with reference to the interlock ring218. When the IM rod 304 is inserted within the IM guide 200, theinterlock knob 242 is positioned within one of the plurality of flutes310 which prevents the IM guide 200 from rotating with respect to the IMrod 304. Therefore, a surgeon can easily manipulate both the IM guide200 and the rod 304 when the rod 304 is inserted through the guide 200.

The diameter of the rod 304 is preferably slightly smaller than thediameter of the drill bit which is used to form the hole 302 whichaccesses the patient's IM canal. The diameter of the rod 304 ispreferably approximately 1 millimeter smaller than the diameter of thehole 302. There are two principal motivations for making the diameter ofthe rod 304 slightly less than the diameter of the hole 302. The firstis to reduce the amount of pressure which is produced within the IMcanal when the rod 304 is inserted therein. As is known, pressurizationof the canal can lead to an increase of fat emboli in the blood stream,which can cause significant health problems. The second principalpurpose for making the IM rod 304 with a smaller diameter than the hole302 is to allow the IM rod to be principally guided by the patient's IMcanal and therefore follow the patient's anatomic axis, and not beguided by the shape or orientation or position of the hole 302. Bykeeping the diameter of the rod 304 smaller than the diameter of theaccess hole 302, the IM rod 304 follows the patient's IM canal ratherthan the shape of the hole 302.

After the surgeon drills the hole 302 in the patient's distal femur end,the surgeon assembles the red 304 into the IM guide 200 and places theassembled rod and guide over the distal femur end, as shown in FIG. 5.The rod 304 is inserted through the hole 302 and pushed into thepatient's IM canal as shown. The rotation of the alignment guide 200about the distal femur end is controlled by inserting a plurality ofpins 312 through the plurality of holes 226 in the base 202 of the guide200. The IM guide 200 can be secured to the distal femur end byinserting the pins 312 through the base 202 and into the patient'sdistal femur bone. A surgeon will typically know when the alignmentguide 200 is correctly placed when an equal amount of medial and lateralfemoral condyles are exposed posterior to the guide 200. When placingthe guide 200 adjacent the patient's distal femur end, the surgeonshould take into consideration the existence of bony anomalies.

Once the surgeon is satisfied with the placement of the IM guide 200 onthe patient's distal femur end, a distal femoral cutting guide 306 canbe attached thereto. As shown in FIG. 5, the distal femoral cuttingguide 306 includes a receptacle 314 which is shaped to receive thedistal femoral resector attachment rod 204 of the alignment guide 200.

The attachment rod 204 includes an insertion canal 316 (best shown inFIGS. 2 and 3) on the femur facing surface of the rod 204. The insertioncanal is shaped to receive a small knob formed along the inner diameterof the receptacle 314 of the cutting guide 306. When the knobs in theinner diameter of the receptacle 314 is placed into the insertion canal316 of the attachment rod 204, the guide 306 is inhibited from rotatingaround the rod 204. Therefore, once the guide 306 is placed over the rod204, the guide 306 is locked into position by the rod 204.

The attachment rod includes a plurality of detents 318 (shown in FIGS.2, 3, and 5) on a top-facing surface. As shown in FIG. 2, the attachmentrod 204 preferably includes five detents 318 along its top-facingsurface opposite the insertion canal 316. The detents 318 are preferablyspaced apart at 1 millimeter increments. The detents 318 give a surgeonflexibility in positioning the distal femoral cutting guide 306 alongthe attachment rod 204. By aligning a front-facing surface 320 of theguide 306 with a selected detent 318, the surgeon can determine how farto displace the distal femoral cutting guide 306 from the base 202 ofthe alignment guide 200. The more that the surgeon displaces the cuttingguide 306 from the base 202 of the alignment guide 200, the more bonethe surgeon can remove from the patient's distal femur end. As shown inFIG. 5, the cutting guide 306 includes a perpendicular cutting slot 322which is shaped to receive a cutting blade (not shown). Daring use, oncethe cutting guide 306 is properly positioned over the patient's distalfemur end, the surgeon inserts the cutting blade through theperpendicular cutting slot 322 and removes bone from the patient'sdistal femur end. Alternatively, some surgeons dislike using a slottedcutting guide and prefer cutting along a flat surface. The presentinvention facilitates use of both a slotted and flat surface cuttingguide, as shown in FIG. 5. The detents 318 in the attachment rod 204allow a surgeon to displace the cutting guide 306 further along thepatient's femur to a position which aligns the flat surface 320 of theguide 306 properly. The detents 318 allow a surgeon to displace thecutting guide 306 to a position where the surface 320 of the guide 306can be used as a guide for the cutting blade rather than the slot 322.Thus, the present invention facilitates use of a cutting guide 306 bysurgeons who prefer to use cutting slot guides similar to the cuttingslot 322 and also by surgeons who prefer to use a flat surface cuttingguide similar to the flat surface 320.

Once the cutting block 306 is placed over the attachment rod 204, thesurgeon can properly align the cutting block 306 with the patient'smechanical axis. With the rod 304 inserted through the IM alignmentguide 200 and the IM canal as shown in FIG. 5, the surgeon unlocks theinterlock ring 218 from the top-facing interlock unit 216 of theadjustment rod 212 by rotating the locking knob 220 counterclockwiseabout the threaded end 230 of the rocker unit 208. After rotating thelocking knob 220, the interlock ring 218, and more specifically theinterlock knob 245, is disengaged from the top-facing unit 216 and thenotch 236 into which the knob 245 was inserted. Once the interlock ring218 is freed from the top-facing unit 216 of the adjustment rod 212, thesurgeon can rotate the adjustment rod 212 so that the interlock knob 245aligns with a desired one of the notches 236. As described above withreference to FIG. 4, the notches 236 are spaced apart in increments thatdetermine the rotational displacement of the adjustment rod 212 aboutthe rocker unit 208. Because the rotational displacement of theadjustment rod 212 with respect to the rocker unit 208 determines thepoints of contact of the displacement pins 210 with the inclined annulargroove 256 (FIG. 4), the degree of rotational displacement of theadjustment rod 212 determines the angle that the base 202 makes withrespect to the adjustment rod 212 and the rocker unit 208. In thepreferred embodiment, the plurality of notches 236 in the top-facingunit 216 are spaced apart at intervals which correspond to 1° angulardisplacements of the base 202 with respect to the rod 212. As shown inFIGS. 4 and 5, the top-facing unit 216 preferably includes markingswhich correspond to the angular displacements that the base 202 makeswith the rod 212 when the knob 245 is inserted within a selected notch236 corresponding to that marking. For example, in the preferredembodiment, the notches 236 have corresponding labels three (3) to nine(9). Each number or marking represents the angle that the base 202 makeswith respect to the adjustment rod 212 and the IM canal when the knob245 is placed into a corresponding notch 236. There are notches 236 andcorresponding markings on both sides of the neutral starting positionnotch 236. As shown in FIG. 5, the top-facing unit 216 is inscribed withmarkings for use of the present invention in a surgery on a right leg ofa patient. FIG. 6 shows a different view of the top-facing trait 216showing markings corresponding to notches 236 for use in surgery on apatient's left leg. Thus, the present invention can be used to align thecutting guide 306 with the mechanical axis for both a left and rightleg. The surgeon simply rotates the adjustment rod 212 either clockwise(when operating on a right leg) from a top center position orcounterclockwise (when operating on a left leg) from a top centerposition so that the knob 245 of the locking ring 218 is inserted intothe notch 236 which corresponds to the previously determined angulardifference between the patient's mechanical and anatomic axes.

For example, if the difference between the patient's mechanical andanatomic axes is 6°, and the surgeon is operating on the patient's rightleg, with the IM guide 200, the IM rod 304 and the cutting block 306assembled as shown in FIG. 5, the surgeon takes the following steps toalign the cutting guide 306 with the patient's mechanical axis. Thesurgeon first releases the interlock ring 218 from the top-facinginterlock unit 216 by rotating the locking knob 220 counterclockwiseapproximately one or two revolutions. The surgeon then rotates theadjustment rod 212 clockwise so that the locking knob 245 of the ring218 is aligned with the notch 236 corresponding with the marking "R-6".The surgeon then rotates the locking knob 220 clockwise about thethreaded end 230 until the locking ring 218 and knob 245 are fullyinserted within the selected notch 236. Due to the operation of thedisplacement pins 210 as described above with reference to FIG. 4, thebase 202 is forced into an angular displacement with the rod 212, rockerunit 208, and IM rod 304 exactly equal to 6°. Because the rod 304 isfully inserted within the IM canal of the patient, and because the IMcanal corresponds to the patient's anatomic axis, the base 202 istherefore forced into an angle which is 6° with respect to the patient'sanatomic axis. Because the attachment rod 204 is perpendicular to thebase 202, the attachment rod 204, and thus the cutting guide 306, alsomakes a 6° angle with respect to the IM canal.

Accordingly, by simply rotating the adjustment rod 212 to align adesired notch 236 with the knob 245 of the interlock ring 218, thesurgeon can quickly and easily align the cutting guide 306 with thepatient's mechanical axis. If the surgeon determines that the alignmentis inaccurate, realignment is quickly and easily accomplished using thepresent invention without the need to interchange parts or remove therod. The IM guide 200, the IM rod 304, and the cutting guide 306 can allbe left assembled as shown in FIG. 5 while the surgeon realigns thecutting guide 306. Therefore, operating-room time is decreased, whichsubsequently reduces the health risks to the patient and the costsassociated with knee replacement surgery. To realign the cutting guide306, the surgeon simply rotates the locking knob 220 counterclockwiseone or two rotations to release the locking ring 218 from the rod 212.The rod 212 can thus be rotated to malign a new notch 236 with the knob245. The process is repeated as described above until the surgeon issatisfied with the alignment. Once the surgeon determines that thecutting guide 306 is properly aligned, the cutting guide 306 can besecured to the patient's femur using securement pins 321.

Once the distal femoral cutting guide 306 is positioned and affixed tothe patient's femur, the IM rod 304 and the IM guide 200 can be removedfrom the femur. Once the IM guide 200 and the IM rod 304 are removed,the distal femoral cutting guide 306 can be more securely affixed to thepatient's femur using additional securement pins 321. Thereafter, thesurgeon inserts a cutting blade through the cutting slot 322 formedthrough the distal femoral cutting guide 306. The saw blade (not shown)is then used appropriately to cut through the distal femur end in knownfashion. This cut is perpendicular to the patient's mechanical axis andis made at a depth to the resection or cut in an amount of bone as willbe replaced by the thickness of the femoral component of the kneeprosthesis. Alternatively, the surgeon can cut through the distal femurend using the front-facing surface 320 of the cutting guide 306 as aguide. The cut surface must be flat to ensure a proper fit of theimplant. The cut surface is then checked for flatness and, if necessary,is further shaped to ensure that the surface is completely flat andadequately positioned.

Referring now to FIG. 6, a quick attach/quick release sighting tool 400is shown for use with the present alignment guide 200 and cutting guide306. Once the surgeon properly aligns the cutting guide 306 with thepatient's mechanical axis (shown in FIG. 6 as dotted line 402), thesurgeon can externally verify proper alignment using the quickattach/quick release sighting tool 400. The sighting tool 400 has aplurality of openings 404 shaped to receive a sighting rod 406. With theguide 306 properly aligned as described above with reference to FIG. 5,the surgeon attaches the quick attach/quick release sighting tool 400 tothe guide 306 as shown in FIG. 6 and as described in more detail belowwith reference to FIGS. 7a and 7b. When the sighting tool 400 isattached to the guide 306 as shown in FIG. 6, the openings 404 areparallel with the attachment rod 204 (FIG. 5) and therefore may be usedto verify that the cutting slot 322 of the guide 306 is perpendicular tothe patient's mechanical axis 402. To verify that the cutting slot 322is perpendicular to the patient's mechanical axis 402, the surgeoninserts the sighting rod 406 through the openings 404. The surgeon thenverifies that the sighting rod 406 aligns with the center of thepatient's femoral head 102. If the sighting rod 406 properly aligns withthe center of the femoral head 102, the surgeon removes the IM guide200, the IM rod 304, the sighting rod 406 and the sighting tool 400 fromthe patient's knee. The surgeon then cuts the distal femur end asdescribed above.

However, if the sighting rod 406 does not properly align with the centerof the femoral head 102, the surgeon can quickly malign the cuttingguide 306 by manipulating the locking knob 220 and the manual adjustmentrod 212 appropriately as described above with reference to FIGS. 4 and5.

FIGS. 7a and 7b show details of the attach and release mechanism used toattach and release the sighting tool 400 to the distal femoral cuttingguide 306. As shown in FIG. 7a, the sighting tool 400 is a cylindricaland substantially elongate tool which has a pair of juxtaposed matingtines 408 formed into a distal end of the sighting tool 400. The matingtines 408 are preferably formed from one solid piece 410 of the matingtool 400. As shown in FIG. 7a, when left undisturbed by an externalforce, mating ends 412 of the mating tines 408 are substantiallyproximate one another. However (shown in phantom in FIGS. 7a and 7b),the mating ends 412 can be forced apart in an elastic fashion by anelliptical cam 414 rotated between the mating ends 412 using a rotationlever 416. Because the cam 414 is elliptical, the ends 412 can be forcedaway from one another by rotating the lever 416 either clockwise orcounterclockwise, as shown in FIG. 7b.

As shown in FIG. 7a, the mating ends 412 of the tines 408 includeinsertion knobs 418 and insertion dovetails 420. The insertion knobs 418and dovetails 420 are used to interlock the sighting tool 400 with thecutting guide 306. As shown in FIGS. 5 and 6, the cutting guide 306includes a sight rod slot 422 which is shaped to receive the insertionknobs 418. Thus, a surgeon can quickly attach the cutting guide 306 tothe sighting tool 400 by inserting the insertion knobs 418 into thesight rod slot 422. The sight rod slot 422 guides the insertion knobs418 as the surgeon rotates the elliptical cam 414 using the lever 416.As shown in FIG. 7b, with the insertion knobs 418 properly alignedwithin the slot 422 of the guide 306, the surgeon rotates the lever 416so that the cam 414 pushes the tines 408 away from one another. Thedovetails 420 are shaped to interlock with an interlock slot 424 formedinto a top-facing surface of the cutting guide 306. Thus, as the surgeonrotates the lever 416, the sighting tool 400 mechanically interlockswith the cutting guide 306 due to the interlocking force (produced bythe cam 414) of the dovetails 420 against the locking slots 424. Theinterlocking force maintained by the cam 414 is easily disengaged byrotating the lever so that the cam 414 is in a neutral position, asshown in FIG. 7a. Thus, the present invention provides a mechanism forfacilitating the quick attachment and release of a sighting tool 400from the cutting guide 306. The length of the sighting tool allows it tobe used to assure rotational alignment of both the guide and othercomponents which can be attached to the tool.

An improved intramedullary alignment guide and method for use thereofhas been described. The present alignment guide provides a means forpositioning a distal femoral cutting guide by a range of angles relativeto the anatomic axis which accommodates various patient anatomies. Usingthe patient's intramedullary canal as a reference, the present IM guideprovides a mechanism for ensuring that a distal femoral cutting guide isperpendicular with the patient's mechanical axis. The IM guide is easilyassembled, can be used in knee surgeries on both right and left legs,and can be used to easily and quickly properly align the cutting guidewith the patient's mechanical axis. An external alignment checkingsystem using a quick attach/quick release sighting tool has also beendescribed. The sighting tool is used with the present IM alignment guideto verify proper alignment of the cutting guide with the distal femurend.

A number of embodiments of the present invention have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the invention.Accordingly, it is to be understood that the invention is not to belimited by the specific illustrated embodiment, but only by the scope ofthe appended claims.

We claim:
 1. A femoral alignment guide for positioning a distal femoralcutting guide at an angle which is perpendicular to a patient'smechanical axis, including:(a) a base having a plurality of securementholes formed therethrough for securing the base to a distal femur end ofa patient, wherein the base includes an attachment rod shaped to receivea distal femoral cutting guide; and (b) an angular adjustment meanshaving a longitudinal axis, pivotally and rotationally secured to thebase, wherein rotation of the adjustment means pivots the base, andwherein rotation of the adjustment means about the axis deflects thebase in accordance with the rotational position of the angularadjustment means to adjust the angle between the base and the axis. 2.The femoral alignment guide of claim 1, wherein the angular adjustmentmeans comprises:(a) a substantially elongate rocker unit pivotallycoupled to the base at a first end; and (b) a manual adjustment rodfitted over the rocker unit, wherein the rod has a first and a secondend, and wherein the first end includes a plurality of spaced apartangular displacement positions, each position corresponds to a selectedangular displacement of the base with respect to the adjustment rod, andwherein a user selects a desired angular displacement of the base withrespect to the adjustment rod by rotating the adjustment rod about therocker unit until a desired position is selected.
 3. The femoralalignment guide of claim 1, wherein the attachment rod includes aplurality of spaced apart detents, wherein the detents correspond todistances for offsetting the distal femoral cutting guide from the base.4. A femoral alignment guide for aligning a distal femoral cutting guideto a patient's mechanical axis, including:(a) a base having a pluralityof securement holes formed therethrough for securing the base to adistal femur end of the patient, wherein the base includes an attachmentrod shaped to receive a distal femoral cutting guide; (b) asubstantially elongate rocker unit pivotally coupled to the base, therocker unit having a first end; (c) an angular displacement means; and(d) a manual adjustment rod rotationally and coaxially fitted over therocker unit, wherein the adjustment rod has a first and a second end,and wherein the first end includes a plurality of circumferentiallyspaced apart angular displacement notches and the second end engages theangular displacement means so as to deflect the rocker unit and coaxialadjustment rod with respect to the base upon rotation of the adjustmentrod, wherein the rotational position of each notch corresponds to aselected angular displacement of the base with respect to the adjustmentrod, and wherein a user selects a desired angular displacement of thebase with respect to the adjustment rod by rotating the adjustment rodabout the rocker unit until a desired notch is engaged.
 5. The femoralalignment guide of claim 4, further including:(a) an angulardisplacement means, positioned at the second end of the adjustment rod,wherein the angular displacement means deflects the base into thedesired angular displacement with respect to the adjustment rod.
 6. Thefemoral alignment guide of claim 4, wherein the angular displacementmeans comprises an annular groove and a plurality of displacement pinsinserted therein, and wherein the annular groove has a depth whichvaries with the rotational displacement of the adjustment rod about therocker unit, and wherein the displacement pins deflect the rocker unitinto the desired angular displacement with respect to the base.
 7. Thefemoral alignment guide of claim 4, wherein the base is substantiallyflat, and wherein the base has a hole drilled therethrough for receivingthe first end of the rocker unit.
 8. The femoral alignment guide ofclaim 7, further including pivot pins mounted through the hole in thebase and the first end of the rocker unit, wherein the rocker unitpivots about the pivot pins.
 9. The femoral alignment guide of claim 4,wherein the rocker unit and the adjustment rod are substantially hollow.10. The femoral alignment guide of claim 9, further including:(a) anintramedullary rod, inserted through the rocker unit, the adjustment rodand the base, wherein the intramedullary rod is configured to beinserted into a patient's intramedullary canal, wherein theintramedullary rod aligns the adjustment rod with the intramedullarycanal, and wherein the selected angular displacement of the base withrespect to the adjustment rod is substantially equal to an angle thatthe patient's mechanical axis makes with respect to the intramedullarycanal.
 11. The femoral alignment guide of claim 10, furtherincluding:(a) an alignment verification means, coupled to the cuttingguide, for verifying that the selected angular displacement of the basewith respect to the adjustment rod is substantially equal to the anglethat the patient's mechanical axis makes with respect to theintramedullary canal.
 12. The femoral alignment guide of claim 11,wherein the alignment verification means comprises a substantiallyelongate sighting tool and a sighting rod, and wherein the sighting toolincludes a plurality of sighting holes for inserting the sighting rodtherethrough.
 13. The guide of claim 12, wherein the sighting holes areround, and further comprising slotted sighting holes.
 14. The guide ofclaim 13, wherein the slotted sighting holes allow placement of thesighting rod through the holes in an inclined position.
 15. A method forpositioning a distal femoral cutting guide into an angle which isperpendicular to a patient's mechanical axis, including the steps of:(a)determining an angle that the patient's mechanical axis forms withrespect to the patient's intramedullary canal; (b) positioning anintramedullary alignment guide to a distal femur end of a patient'sfemur, wherein the alignment guide includes:(1) a base including anattachment rod shaped to receive a distal femoral cutting guide, and (2)an angular adjustment means, pivotally secured to the base, whereinrotation of the angular adjustment means pivots the base about an axiswhich is coincident with the intramedullary canal of the patient, andwherein the adjustment means deflects the base into a selected anglewith respect to the intramedullary canal of the patient; (c) insertingan intramedullary rod through the alignment guide and into the patient'sintramedullary canal; (d) rotating the angular adjustment means toselect an angle which is equal to the angle that the patient'smechanical axis forms with respect to the patient's intramedullarycanal; (e) placing the distal femoral cutting guide over the attachmentrod; and (f) securing the cutting guide to the patient's femur.
 16. Themethod of claim 15, further including the step of verifying that thedistal femoral cutting guide is perpendicular with the patient'smechanical axis.